Power assisted brake

ABSTRACT

A hydraulic brake system with a booster for assisting the brake actuating force, the booster control valve being a slide valve mounted in a central bore in the actuating piston and connecting a pressure accumulator to a pressure chamber behind the piston when a slide, which is also mounted in the bore in the piston, opens the valve upon actuation of the brakes.

I United States Patent [15] 3,657,887 Ostwald [4 1 Apr. 25, 1972 [54]PQWER ASSISTED BRAKE [56] References Cited [72] Inventor: Fritz Ostwald,Buchschlag, Germany UNITED STATES PATENTS [73] Assignee: InternationalTelephone and Telegraph 2,410,269 10/1946 Chouings ..60/54.6 PCorporation, New York, NY. 2,544,042 3/1951 Pontius ..60/54.6 P [22]Filed: 1970 Primary Examiner-Edgar W, Geoghegan 21 APPL 14 048 AssistantExaminerA. M. Zupcic Attorney-C. Cornell Remsen, Jr., Walter J. Baum andPaul W. Hemminger [30] Foreign Application Priority Data 57 1 ABSTRACT Ahydraulic brake system with a booster for assisting the brake actuatingforce, the booster control valve being a slide valve mounted in acentral bore in the actuating piston and connecting a pressureaccumulator to a pressure chamber behind the piston when a slide, whichis also mounted in the bore in the piston, opens the valve uponactuation of the brakes.

1 Claims, 2 Drawing Figures MASTER CYL/NDER 77 RESERVOIR POWER ASSISTEDBRAKE BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to hydraulic brake systems with a booster forassisting the brake actuating force and particularly to brake systems ofthis type in which a valve in the master cylinder connects a pressureaccumulator to a pressure chamber behind the master cylinder piston whenthe brakes are applied to boost the brake actuating force.

2. Description of Prior Art German Pat. No. l 226 444 discloses a brakebooster system which uses an accumulator and a booster pump. A hollowactuating piston is disposed in the master cylinder, the latterconsisting of an operating piston and a control member. The hollowactuating piston is displaced by external force until the front of thehollow actuating piston, after having overcome a certain clearance,abuts against a valve seat on a bushing inserted in the operatingpiston. Pressure medium flow from a booster pump through the mastercylinder to a reservoir is thereby interrupted and the pressure mediumconveyed by the pump is applied to the annular surface of the actuatingpiston as well as to the effective surface of the operating piston. Apin which is rigidly fixed to the operating piston extends with wideclearance into the inner bore of the actuating piston and actuates alever when the piston is displaced to move a rocker-arm bracket with apush rod mounted thereon, which, after overcoming a certain clearance,opens a check valve in the line leading to the pressure accumulator.Since this high-pressure line communicates with the pressure medium flowvia a longitudinal bore in the housing of the control member, theactuating piston and the operating piston will be acted upon by theaccumulator pressure after the check valve is open.

German Pat. No. l 232 827 discloses a brake booster which is completelyseparated from the master cylinder. A first hydraulic power source ispermanently connected to a chamber in the booster control communicatingwith the master cylinder. In the rest position the chamber is alsoconnected to the reservoir via a bore in the booster control valve body,the latter being accommodated in a bushing. The feed line of a pressureaccumulator terminates in the annular chamber in the bushing, thechamber being closed towards the master cylinder by means of the seatvalve. Upon actuation of the system an opening provided in the actuatingmember caps the cylindrical end of the valve body and thus interruptsthe pressure medium flow to the reservoir so that the full pressureexerted by the first pressure medium source is applied to the mastercylinder piston. Upon further displacement of the actuating member thespring-loaded valve body is lifted from its seat thereby providing aconnection between the pressure accumulator and the master cylinder.

The arrangement of the power cylinder unit and the pressure controlunit, either axially one after the other as in German Pat. No. l 226444, or in completely separate housings as in German Pat. No. l 232 827,requires an undesirably large amount of space. In addition, a number ofmovable seals permanently subject to the accumulator pressure arenecessary and this reduces the sensitivity of the system response.

SUMMARY OF THE INVENTION An object of this invention is to provide amaster cylinder and brake booster which requires less space than priorart devices.

Another object of this invention is to provide a compact master cylinderwhich requires less seals, particularly such seals which are subject tothe accumulator pressure than the prior art devices, whereby thesensitivity of system response is increased.

These objects are achieved by providing a master cylinder with a hollowactuating piston into which the entire auxiliary pressure control isfitted.

In the embodiments shown in the accompanying drawings a passage in thebody of the hollow operating piston has one end permanently connected tothe accumulator and the other end connected to a spring-loaded slidevalve leading to the inner bore of the piston which communicates withthe actuating chamber for the piston. An actuating member within thepiston closes a connection between the reservoir and the actuatingchamber and opens the slide valve when the brakes are applied.

The accumulator is connected to the passage in the piston either by aflexible hose or an axially extending annular supply chamber in thehousing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view ofa hydraulic brake master cylinder and booster control embodying thepresent invention.

FIG. 2 is a partial sectional view of a hydraulic brake master cylinderand booster control showing another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 thereis shown a master cylinder 15 having an operating piston 1. A slide 2and a valve member 3 are slidably arranged in a central bore in theoperating piston. The valve member 3, which can be opened by the slide2, is held against a valve seat 5 in the piston by a spring 4. Aflexible hose 7 having one end connected to a pressure accumulator 29supplies hydraulic fluid to an annular chamber 8 in the valve member 3via a passageway 6 in the piston l.

The slide 2 has a stepped end 9 which lifts the valve 3 from its seatwhen the brakes are actuated by the movement of the slide in thedirection A shown in the drawing. In the unbraked condition, the slide 2is held in the position shown in FIG. 1 by means of a spring 10 whichbears against the step in the slide and an abutment provided in theinner bore of the piston. A clearance 11 exists between end 9 of theslide and the valve member 3 in the unbraked condition. An annularpressure chamber 14 between the master cylinder 15 and piston 1 isconnected to the longitudinal bore 12 in the slide 2 by openings 13. Alongitudinal bore 12 in the valve member 3 continues the bore 12' andconnects with the downstream side of the valve 3. Abutments 21 and 22provided on the piston wall and the cylinder wall in the annular chamber14 limit the movement of the piston l. The annular surface 16 of thestepped piston forms thesurface to which the auxiliary pressure isapplied and is sealed towards the piston and the cylinder wall by meansof a gasket. In the position shown the master cylinder reservoir 17 isconnected to annular chamber 14 via bore 28, annular chamber 18,transverse bore 19 in the piston 1, clearance 11, longitudinal bore 12'and holes 13.

The invention operates as follows: in the initial position of the pistonand the slide as shown in FIG. 1, the reservoir is connected to thepressure chamber 14 while the valve member 3 is kept in closed positionagainst the seat 5 by the spring 4. If the piston is to be moved in thedirection of actuation, i.e., in the direction A, the slide 2 has to bemoved inthe same direction by external force on the: push rod 30.Thereby the connection between the reservoir 17 and the annular chamber14 through the concentric bore 12' of the slide is closed as the annularface of the slide end 9 engages the op posed surface of the seat valve 3to eliminate the clearance 11. Upon further movement of the slide 2, thevalve 3 is lifted from its seat 5 thereby opening the passage from thechannel 6 into the inner bore of the piston. The pressure medium thenflows from the accumulator through the channel 6 and the open valve 3into the inner bore of the hollow piston 1 and is applied to the bottomsurface of the piston 1 which is dis placed as a consequence thereof.This causes the abutment 21 of the piston 1 to be lifted from theabutment 22 of the inner cylinder wall, thus enabling the pressuremedium to flow through the bores 12, 12' and 13 into the enlargedannular chamber 14 and to act against the annular surface 16 of thepiston. the annular surface being fitted with a gasket. As is wellknown, a reaction force arises at the surface of the seat valve. Hence,the power transmission is dependent of the ratio between the seat valvesurface and the effective surface 16. If the slide 2 moves in theopposite direction thereby restoring the connection between the annularchamber 14 and the reservoir 17 via the slot located between the slideend 9 and the seat valve 3, this will cause the pressure in the annularchamber 14 to reduce, and the stepped piston will return to its initialposition by spring action.

Besides the compact construction which this invention provides, it is aspecial advantage of the invention that seals can be omitted which areotherwise permanently or continuously exposed to the high accumulatorpressure in the actuated and unactuated position of slide 2 and reducethe sensitivity of response of the unit. In the illustration shown inFIG. 1 the only seal that is exposed continuously to high accumulatorpressure is seal 31.

The embodiment of the invention shown in FIG. 2, which is the same asthat shown in FIG. 1 except as described hereinbelow, eliminates thenecessity of the flexible hose 7 between the accumulator and the passage6. An inlet 24 which is connected to an accumulator 29 communicates withan axially extending annular chamber 26 formed between the cylinder 23and the piston 1 via bore 25. An opening 27 in the piston wall connectsthe chamber 26 to the channel 6. In this case a seal between thecylinder and piston must be provided on either side of the annularchamber 26.

It will be appreciated that the invention illustrated and describedherein may be modified by those skilled in the art without deviatingfrom the spirit and scope of the invention as set forth in the followingclaims.

I claim as my invention:

1. A power assisted hydraulic brake comprising:

a reservoir;

a pressure accumulator;

a hollow cylindrical housing having a longitudinal axis;

an operating piston disposed coaxially of said longitudinal axis insliding engagement with said housing and extending from a first pointoutside said cylindrical housing to a second point inside saidcylindrical housing, said piston including a first bore disposedcoaxially of said longitudinal axis, a longitudinal passage disposedwholly within said piston extending from a third point adjacent saidfirst point to a fourth point adjacent said second point and beingradially spaced from said longitudinal axis and said first bore, anannular surface extending outwardly from the outer surface of saidpiston intermediate said first and second points to which pressure isapplied from said accumulator and a valve seat formed on the innersurface of said first bore adjacent said fourth point;

a movable actuating slide disposed coaxially of said longitudinal axisand in sliding engagement with the inner surface of said first bore,said slide having an actuating surface, a second bore disposed coaxiallyof said longitudinal axis being open at one end thereof and closed atthe other end thereof adjacent said actuating surface and a transversepassage through the wall of said slide adjacent said actuating surfacefor communication between said second bore and said annular surface;

a movable valve member disposed coaxially of said longitudinal axis andin sliding engagement with the inner surface of said first bore, saidvalve member having one end thereof adjacent said one end of said slidenormally spaced from said one end of said slide to provide a clearancepassage, a valve closing element disposed on the other end of said valvemember to normally seat on said valve seat and a third bore disposedcoaxially of said longitudinal axis and extending completely throughsaid valve member in communication with said second bore;

a first chamber disposed between the outer surface of said valve memberand the inner surface of said piston in communication with saidlongitudinal passage adjacent said second point and said valve seat; asecond chamber disposed between the inner surface of said housing andthe outer surface of said piston in communication with said reservoirand said clearance passage;

a flexible hose connected between said accumulator and said longitudinalpassage adjacent said third point;

means to actuate said slide to close said clearance passage to interruptfluid flow to said reservoir from said annular surface through saidtransverse passage, said second bore, said clearance passage and saidsecond chamber and to move said valve member to unseat said valveclosing member to permit said accumulator to communicate with saidannular surface through said longitudinal passage, said first chamber,said valve seat, said second and third bore and said transverse passage;and

only a single seal subjected continuously to the pressure of saidaccumulator during both the actuated and unactuated position of saidslide, said seal being disposed between the outer surface of said valvemember and the inner surface of said first bore intermediate said firstchamber and said clearance passage.

1. A power assisted hydraulic brake comprising: a reservoir; a pressure accumulator; a hollow cylindrical housing having a longitudinal axis; an operating piston disposed coaxially of said longitudinal axis in sliding engagement with said housing and extending from a first point outside said cylindrical housing to a second point inside said cylindrical housing, said piston including a first bore disposed coaxially of said longitudinal axis, a longitudinal passage disposed wholly within said piston extending from a third point adjacent said first point to a fourth point adjacent said second point and being radially spaced from said longitudinal axis and said first bore, an annular surface extending outwardly from the outer surface of said piston intermediate said first and second points to which pressure is applied from said accumulator and a valve seat formed on the inner surface of said first bore adjacent said fourth point; a movable actuating slide disposed coaxially of said longitudinal axis and in sliding engagement with the inner surface of said first bore, said slide having an actuating surface, a second bore disposed coaxially of said longitudinal axis being open at one end thereof and closed at the other end thereof adjacent said actuating surface and a transverse passage through the wall of said slide adjacent said actuating surface for communication between said second bore and said annular surface; a movable valve member disposed coaxially of said longitudinal axis and in sliding engagement with the inner surface of said first bore, said valve member having one end thereof adjacent said one end of said slide normally spaced from said one end of said slide to provide a clearance passage, a valve closing element disposed on the other end of said valve member to normally seat on said valve seat and a third bore disposed coaxially of said longitudinal axis and extending completely through said valve member in communication with said second bore; a first chamber disposed between the outer surface of said valve member and the inner surface of said piston in communication with said longitudinal passage adjacent said second point and said valve seat; a second chamber disposed between the inner surface of said housing and the outer surface of said piston in communication with said reservoir and said clearance passage; a flexible hose connected between said accumulator and said longitudinal passage adjacent said third point; means to actuate said slide to close said clearance passage to interrupt fluid flow to said reservoir from said annular surface through said transverse passage, said second bore, said clearance passage and said second chamber and to move said valve member to unseat said valve closing member to permit said accumulator to communicate with said annular surface through said longitudinal passage, said first chamber, said valve seat, said second and third bore and said transverse passage; and only a single seal subjected continuously to the pressure of said accumulator during both the actuated and unactuated position of said slide, said seal being disposed between the outer surface of said valve member and the inner surface of said first bore intermediate said first chamber and said clearance passage. 